Investigations on the Wear Rate of Sintering Diamond Core Bit during the Hole Drilling Process of Al2O3 Bulletproof Ceramics

Bulletproof ceramics are usually hard and brittle with high elastic modulus, high compressive strength, and low tensile strength. While machining bulletproof ceramics, severe tool wear makes it difficult to obtain desired machining quality and efficiency, especially in hole drilling. In this work, an intensive experimental study on the overall wear rate of the sintering diamond thin-wall core bit during the hole drilling of Al2O3 bulletproof ceramics (99 wt.%) has been carried out. The quality loss of the bit after each hole drilled was selected for representing the overall wear rate of the bit. Based on experimental data, the influences of the main bit performance and machining process parameters on the overall wear rate of the bit have been analyzed. According to the results discussed, under the test conditions, finer diamond grit, higher diamond concentration, lower number of water gaps, thinner wall thickness, or lower bit load all can decrease the wear rate of the bit. However, within a certain range, the spindle speed has little influence on the overall wear resistance of the bit, but when the spindle speed increases, the machining efficiency can be significantly improved. The results obtained in this work can offer a valuable reference for the use of sintering diamond thin-wall core bits in the hole drilling of bulletproof ceramics.

Surface Integrity of AlSiC Composites Ground by Monolayer Brazed Diamond Wheels

Monolayer brazed diamond wheel were used to grind AlSiC composite with different volume fraction of SiC. The effects of diamond mesh size of the grinding wheels and the volume fraction of SiC in AlSiC composite on the surface integrity of ground AlSiC composite were investigated. It is found that the surface roughness of ground AlSiC composite with 20% SiC is increased with the reduction of diamond grit’s size because of the clogging of diamond wheel. With the increasing of the volume fraction of SiC, there are more fractured and cracked SiC particles on the ground surface of AlSiC composite. On the other hand, the finer diamond grits (70/80) induce the finer fractured SiC particles on the ground surface of AlSiC with 50% and 70% SiC.

Effects of substrate pretreatment and methane fraction on the optical transparency of nanocrystalline diamond thin films

Optical transmittance of the nanocrystalline diamond films has been studied as a function of grain size of the diamond powder used for substrate pretreatment and the methane fraction in the source gas. It has been observed that for CH4 fractions below 13%, the films grown on substrates pretreated with finer diamond powder are more transparent, while this trend reverses for CH4 fractions above 13%. These variations in the transparency of the films correlate very well with their corresponding surface roughness. Nanocrystalline/amorphous diamond films with transmittance of greater than 80% beyond 700 nm and with average surface roughness as low as 61 Å have been obtained for CH4 fractions as high as 42% in the source gas. Interestingly, these films do not show an obvious presence of any graphitic carbon, and the structural ordering of the amorphous sp3-bonded phase also seems to be insensitive to the CH4 content of the source gas.